1. Field of the Invention
The invention relates to a method and an apparatus for minimizing thermoacoustic vibrations in gas-turbine combustion chambers.
2. Discussion of Background
It is known that undesirable thermoacoustic vibrations often occur in combustion chambers of gas turbines. The term “thermoacoustic vibrations” designates mutually amplifying thermal and acoustic disturbances. In the process, high vibration amplitudes may occur and these may lead to undesirable effects, such as, for instance, high mechanical loading of the combustion chamber, increased NOx emission due to inhomogeneous combustion, and even extinction of the flame. This applies in particular to combustion systems having low acoustic damping. In order to ensure a high output with regard to pulsations and emissions over a wide operating range, active control of the combustion vibrations may be necessary.
The fluidic stability of a gas-turbine burner is of decisive importance for the occurrence of thermoacoustic vibrations. The fluidic instability waves arising in the burner lead to the formation of vortices. These vortices, also designated as coherent structures, are important during mixing actions between air and fuel. The dynamics of the coherent structures influence the combustion and the heat release associated therewith. The vortices may therefore lead to periodic heat release of the flame of the burner and thus to pressure fluctuations. In particular, if there is no homogeneous mixing of fuel and air over the entire area of the burner, the development of coherent vortex structures has a considerable effect on the formation of thermoacoustic instability. Thus a further possibility of reducing the tendency of a burner to vibrate is to stablize the flame of the premix burner.